Method for measuring the magnetic saturation profiles of a synchronous machine, and device for the open-loop and closed-loop control of an induction machine

Abstract

The present invention relates to a method for measuring the magnetic saturation profiles of a synchronous machine comprising a rotor and a stator, wherein the synchronous machine is activated by clocked terminal voltages according to a pulse width modulation method and the current of the synchronous machine is measured cyclically. The invention also relates to a device for the open-loop and closed-loop control of an induction machine. The method and device described are used, when putting a synchronous motor into service, to derive rotor position allocation parameters to allow the motor to be controlled without a position sensor.

Description

[0001] Method for measuring the magnetic saturation curves of a synchronous machine and device for controlling and regulating a rotating field machine

[0002] The present invention relates to a method for measuring the magnetic saturation curves of a synchronous machine, comprising a rotor and a stator, wherein the synchronous machine is controlled via clocked terminal voltages according to the pulse width modulation method and the current of the synchronous machine is measured cyclically, as well as a device for controlling and regulating a rotating field machine.

[0003] The described method and device are used to derive rotor position assignment parameters during commissioning of a synchronous motor in order to enable motor control without a position sensor.

[0004] Today's established, high-performance, and highly efficient control of synchronous machines is based on knowledge of the rotor position signal. This is because so-called rotor position feedback enables the use of motor control methods that optimize efficiency and performance, as well as the fulfillment of higher-level tasks such as speed control or positioning. The rotor position is typically measured during operation using a sensor attached to the rotor shaft—the so-called rotor position sensor, or encoder for short.

[0005] Encoders have a number of disadvantages, such as increased system costs, reduced robustness, increased probability of failure and larger installation space requirements, which justify the great industrial interest in obtaining the position signal without using an encoder.

[0006] Methods that make this possible are called “sensorless” or “sensorless” control and are divided into 2 classes:

[0007] 1. Fundamental wave methods evaluate the voltage induced during movement, provide very good signal properties at medium and high speeds, but fail in the lower speed range, especially at standstill.

[0008] 2. Anisotropy methods evaluate the position dependence of the inductance of the machine, which is possible even at low speeds and at standstill.

[0009] The term "machine" is used here in the sense of an "electrical machine," i.e., an electric motor or an electric generator. Machine, motor, and generator are synonymous with respect to the process presented, so the terms can be used interchangeably.

[0010] To assign rotor position values ​​to the fundamental wave and the anisotropy, specific motor parameters are required. This disadvantage compared to an encoder becomes even more significant the more complex and time-consuming the parameter determination process is. Automated self-commissioning of all required parameters therefore contributes significantly to the applicability of an encoderless method.

[0011] While the clear rotor position assignment for anisotropy and fundamental wave has enabled significant advances in sensorless control with regard to general operating behavior and especially with regard to load stability, both approaches require complex parameter sets. This is because the flux and / or inductance / admittance curves are required under the application of large currents (the same overload factor as in operation), which generate correspondingly large torques. The previous parameter determination therefore required a load test bench, where a load machine supports the resulting torque while the parameter measurement takes place.

[0012] The term flux ψ here refers to the magnetic flux linkage 'P minus its remanence component. For zero current, the flux ψ is also zero by definition, while the total magnetic flux linkage 'P, for example in permanent magnet (PM) motors, still has an offset ψ pmIn the context of flux, the term "pulse" refers to the shortest possible impression of a specific flux value, with the term "macroscopic" referring to the magnitude of the flux value: namely, that the flux pulses should produce current values ​​across the entire operating range of the motor, which, depending on the application, can be several times the rated motor current and generally leads to a change in the magnetic saturation state of the motor. In contrast, there are "microscopic" flux pulses, such as those impressed when applying anisotropy methods. These are preferably kept small and are not intended to change the saturation state.

[0013] The presented method determines a parameter set for unambiguous rotor position assignment without the use of a load test bench, i.e., simply by connecting the converter to the synchronous machine. Macroscopic flux pulses are injected, which briefly create magnetic saturation states such as those that occur during operation. This results in corresponding current and torque values. However, due to the short duration of the pulse injection, these do not change the speed and consequently the rotor position sufficiently to have a relevant effect on parameter acquisition. In one embodiment, an additional injection cycle is performed upon reaching the saturation state in order to also obtain the admittance / inductance values ​​at this operating point.

[0014] The following is a general explanation, including optional embodiments of the invention. The following are shown:

[0015] Fig. 1 Time course of voltage u (top), resulting flux ψ (middle) and current i (bottom) each with d- (continuous) and q-component (dashed) during a macroscopic flux pulse.

[0016] Fig. 2 Representation of the current responses of all flux pulses of a commissioning, plotted in normalized dq coordinates (related to the rated motor current), where the flux pulse values ​​are distributed equidistantly and the distorted distribution of the displayed current responses reflects the magnetic nonlinearity.

[0017] Fig. 3 Time course of voltage u (top), resulting flux ψ (middle) and current i (bottom) each with d- (continuous) and q-component (dashed) during a macroscopic flux pulse with additional imprinting of an injection cycle.

[0018] Fig. 4 Representation of the calculated anisotropy vectors for all flux pulses of a commissioning. Based on Fig. 2, each anisotropy vector is plotted by a line emanating from the corresponding current point, with the length unit [500 A / Vs] chosen for illustrative scaling.

[0019] Fig. 5 Time course of voltage u (top), resulting flux ψ (middle) and current i (bottom) each with d- (continuous) and q-component (dashed) during a macroscopic flux pulse with additional imprinting of an injection cycle and subsequent counterpulse for angular momentum compensation.

[0020] The term admittance Y of a synchronous machine refers to the inverse of the inductance L, both of which can be described as a matrix in the case of magnetically anisotropic behavior The superscript generally stands for the coordinate system (CS), in this case stator coordinates (axes a and ß), the subscript describes the quantity in more detail, in this case the relationship of the quantity to the stator winding.

[0021] The transformation matrix T(0) enables the transfer of vectors from one KS to another where in these examples the current vector and the admittance matrix were converted from stator to rotor coordinates (axes d and q) using the rotor angle.

[0022] The anisotropy vector is the following linear combination of the components of the admittance matrix γs s

[0023] (5) and can be converted into a rotor-fixed representation using the transformation matrix T(0) using twice the rotor angle where it has an equivalent relationship to the rotor-fixed admittance matrix

[0024] In addition, for certain processes the isotropic component Y Σ relevant, which can be calculated by a further linear combination which cannot be assigned to any coordinate system. By combining the anisotropy vector and the isotropic component Y, the admittance vector results in the corresponding coordinate nates of the anisotropy vector. Macroscopic flux pulses are impressed, which briefly increase the motor current to a magnitude that can change the magnetic saturation state of the motor. Each flux pulse is preceded by a target flux value, which is taken, for example, from a table. This target flux value is implemented by impressing a voltage-time domain, and the current value that occurs at the end of this voltage-time domain is measured and stored. Fig. 1 shows in the upper graph how, for example, constant voltage values ​​are impressed in the d- and q-direction over a specific time Δt. According to the general equation v > In the middle graph, a linear flux increase results during the constant voltage phases. If a constant voltage value is selected, the time period Δ t for voltage impression simply

[0025] However, non-constant voltage values ​​or different times Δt for d- and q-voltage can also be used, provided that the voltage-time area according to (9) corresponds to the desired flux value.

[0026] Furthermore, the actually impressed voltage can be corrected for known disturbance terms (e.g., resistance and / or converter nonlinearities) that are not included in the calculation of the voltage-time area. Furthermore, the impressed voltage values ​​can preferably be selected as high as possible within the available intermediate circuit voltage (the times Δt correspondingly short) in order to minimize these disturbances.

[0027] The lower graph of Fig. 1 shows an example of how the current increases nonlinearly, which can occur differently in the d- and q-components. This nonlinear increase during a linear flux increase is caused by the magnetic saturation of the iron in the machine and varies qualitatively and quantitatively between different motor types. For a clear rotor position assignment specification according to [1] or [2], it is essential to have data on this nonlinear behavior.

[0028] At the end of the voltage-time domain, the target flux value is established in the flux, and the nonlinearly associated current value is established in the current, which is then recorded by means of a current measurement. Optionally, a small or zero voltage can be temporarily applied after the voltage-time domain, as shown in Fig. 1, to minimize interference during the current measurement (e.g., due to recharging of the motor cable).

[0029] However, the duration of high current should be kept as short as possible, because over this time the torque associated with the pulse is converted into an angular momentum and consequently a rotational movement is created, which must first come to a standstill after the flow pulse has been completed before a next pulse can be impressed.

[0030] Thus, as shown in Fig. 1, each flux pulse ends with a negated voltage-time domain, which quickly returns the flux values ​​and the current to zero. This second voltage-time domain has the same d and q components as the first, but with the opposite sign.

[0031] Finally, the values ​​of the flux pulse and the measured resulting current are assigned to each other and saved as an operating point data pair. The next target flux value is taken from a table, for example, in order to repeat the process for a large number of systematically different flux values. Thus, a large number of macroscopic flux pulses with different d and q components are impressed, and the resulting operating point data pairs are stored in a table. This results in a data set as illustrated in Fig. 2. Each measured current value is plotted here in its d and q components by a point, with 224 flux pulses being impressed. The target flux values ​​were located on a rectangular, equidistant grid (pulses that would have exceeded 250% of the nominal current were omitted), while the arrangement of the current points is significantly distorted.This distortion reflects the magnetic nonlinearity of the motor in question, which in this example was a synchronous reluctance motor. Its symmetry conditions allow measurements in only one quadrant. Synchronous motors with magnets also require measurements at negative d-current.

[0032] In one embodiment, after the current measurement, an injection pattern is run for each macroscopic flux pulse, i.e., while the macroscopic current value is still present. This consists of microscopic flux pulses, which, due to their much smaller voltage-time areas, should not change the saturation state, but are suitable for detecting the value of the local inductance or admittance at this operating point. Therefore, directly after the macroscopic flux pulse, several microscopic flux pulses, i.e., flux pulses that do not significantly change saturation, are injected. These flux pulses are different from one another, add up to zero, and form the injection pattern in their shape and arrangement.

[0033] Fig. 3 shows an example of the imprinting of a square injection pattern, where the microscopic pulses are first injected in the +d direction, then in the +q direction, then in the -d direction, and finally in the -q direction. They have the same magnitude and are orthogonal or antiparallel to each other, so that the injection pattern is a square. However, the technical advantages of this injection pattern described in [3] are not essential for this admittance measurement; any other injection pattern can be used instead.

[0034] As a result of the microscopic voltage-time surfaces, small linear flux increases can be seen in the middle part of Fig. 3, which in turn lead to somewhat larger but also approximately linear current increases. They are approximately linear because the microscopic injection pulses do not significantly change the saturation state.

[0035] The current response to each of the microscopic pulses is recorded, and after completion of the injection pattern, all measured values ​​are converted into inductance, admittance, and / or anisotropy values ​​using the known algorithms of the corresponding injection method, e.g., according to [3]. For example, the dq components of the anisotropy vector from (6) could be calculated as follows: if for A the d-current change due to the first microscopic pulse, for the q-current increase due to the second microscopic pulse etc is used and ψ inj never describes the sum of the voltage-time areas of all microscopic injection flow pulses.

[0036] Optionally, microscopic centering pulses can be applied before the first and after the last microscopic pulse to keep the injection response centered around the macroscopic current measurement. However, it is generally recommended to keep the injection duration as short as possible to minimize the resulting rotational movement.

[0037] Finally, after calculating the inductance, admittance, and / or anisotropy values, these are stored and assigned to the macroscopic pulse, i.e., the flux and / or current value. This sequence is repeated after each macroscopic flux pulse. Thus, the entries for the local admittance or inductance are calculated from the current response to the injection pattern, added to the operating point data pair, and saved.

[0038] As a result, the exemplary data set from Fig. 2 is extended with corresponding inductance, admittance, and / or anisotropy data. For the example motor, this is illustrated in Fig. 4 by black lines, which map the respective anisotropy vector (12) - (13) starting from the corresponding current point in the actual direction and scaled length.

[0039] The angular momentum generation resulting from the macroscopic pulses can be compensated by applying a counterpulse directly following the test pulse, as illustrated by way of example in the right half of Fig. 5. For this purpose, a mirror symmetry of the torque about the d-axis is assumed, which applies to all synchronous motor types regardless of their specific saturation behavior. Consequently, angular momentum compensation can be achieved by applying a second pulse which is identical in magnitude and duration to the first, but where the sign of the q-component of all displayed quantities is reversed, while the sign of the d-component remains the same (cf. Fig. 5 right vs. left). Thus, each macroscopic flux pulse is followed by an associated compensation pulse which has the same d- and a negated q-component in order to minimize the resulting angular momentum.The injection pattern does not need to be repeated because it is mean-free.

[0040] However, various effects (including the influence of resistance and the slight rotor rotation) mean that the counter pulse cannot usually be generated with exactly the same size, so that some angular momentum remains after the counter pulse has ended. In addition, even with perfect angular momentum compensation, the speed would be zero at the end, but the rotor would be rotated relative to its position before the test pulse (initial position). Therefore, the rotor position must be determined again before the next test pulse and the validity of the dq coordinate system (CS) must be restored. In one embodiment, this is achieved by applying a direct current of the order of magnitude of the rated motor current in a defined direction before each macroscopic flux pulse until the resulting oscillating movement has subsided and the rotor is aligned again with the current in its initial position.For this purpose, the dq-KS is not rotated with the rotor during rotor movement, but is initialized only once before the first test pulse and from then on remains firmly aligned with the initial position for the duration of all test pulses. In these fixed dq coordinates, a d-current can then simply be regulated following a test pulse and a parameterizable time can be waited. By specifying the q-current proportional to the q-voltage in these fixed dq coordinates, an additional damping term can optionally be created which allows the oscillation to decay more quickly. The dq-KS can be initialized before the first test pulse using sensorless initial position determination (e.g. according to [4]) in order to minimize the rotor movement as a result of the first DC current injection; or it can be done arbitrarily if the rotor movement is not relevant.

[0041] In another embodiment, the motor shaft is mechanically locked externally before the first test pulse, so that the mechanical stiffness returns the rotor to its initial position after each pulse, eliminating the need for a DC current injection. However, in this case, a sensorless initial position determination (e.g., according to [4]) is required to reliably align the dq-KS with the locked rotor.

[0042] In another embodiment, after each test pulse and decay of the movement, a new sensorless initial position detection is performed, and the dq-KS is realigned for the subsequent pulse. Even though the accuracy of sensorless initial position detection is generally lower than that of alignment by direct current injection, this embodiment can be advantageous if, for example, direct current alignment is not sufficiently possible due to special circumstances, such as high friction or a high reluctance component in the nominal torque of a permanent magnet motor.

[0043] After all data pairs of flux and current (see Fig. 2) and, if applicable, admittance (see Fig. 4) have been saved, the position assignment parameters are finally derived. A rule for calculating values ​​apart from / between / outside the data pairs is selected as the basis for this. This can be linear or non-linear interpolation / extrapolation, adoption of the nearest value, an analytical or numerical approximation, or another type of smoothing rule. Regardless of the choice of rule, the term interpolation is used below for the selected rule. In one embodiment, simple rotor position assignment parameters are calculated from the table entries using interpolation. For this purpose, the load dependence of, for example, the secant inductance and the anisotropy shift is determined; these are exemplary parameters for simple sensorless methods.To do this, a current trajectory is first selected to be used in operation (e.g., the maximum torque per ampere curve, or MTPA for short). Then, several current points are taken from this trajectory, and the value for each of these points is calculated using the stored data pairs. of the flow and, if applicable, the value of the anisotropy nterpolated. From this, the value of the secant inductance is then calculated for each of these points, such as ( 15) and the value of the anisotropy shift calculated and stored with the selected current point. The result is a table of these parameters along the surge current trajectory, which can then be used to interpolate the load-dependent value of the respective parameter during subsequent operation. Analogous to (15) or (16), other parameters directly related to the flux or amittance can also be interpolated if they are required by a process during operation.

[0044] In another embodiment, unique rotor position assignment parameters are derived from the table entries using interpolation and SFC calculation. For this purpose, so-called SFC trajectories of the flux and / or admittance are derived from the stored data pairs, which form the basis for methods of unique position assignment [1] and / or [2]. According to [1] and [2], these SFC trajectories describe the course of the flux or admittance over the changing rotor position when the current is fixed in stator coordinates. Any fixed current in stator coordinates i s s results in the following rotor position-dependent value i in rotor coordinates s r (17)

[0045] With this rotor position-dependent current in rotor coordinates, an interpo- lation is carried out on the stored data pairs in order to determine a rotor position-dependent flux or a rotor position-dependent admittance or These interpolated values ​​are then transformed back to stator coordinates to obtain the SFC trajectories of flux and admittance or to obtain

[0046] In (19) the remanence component of the magnetic flux linkage is added, so that ψs s is now a complete magnetic flux linkage, while all previous flux values ​​ψ were by definition free of remanence and consequently zero for zero current.

[0047] These SFC trajectories and y and y are the basis for the Derivation of a unique rotor position assignment, which is then carried out according to [1] or [2].

[0048] Bibliography

[0049] [1] P. Landsmann, D. Paulus and S. Kühl, “Method and device for controlling a synchronous motor without a position sensor by means of a unique assignment of the admittance or inductance to the rotor position.” DE, WO Patent DE102018006657A1 , 17 8 2018.

[0050] [2] P. Landsmann, D. Paulus and S. Kühl, “Method and device for controlling a synchronous machine without a position sensor by means of a unique assignment of the flux linkage to the rotor position.” EP, WO Patent EP3826169A1 , 25 11 2019.

[0051] [3] P. Landsmann, “Method for identifying the magnetic anisotropy of an electric rotating field machine.” DE, EP, WO Patent DE102015217986A1 , 18 09 2015.

[0052] [4] J. Holtz, “Initial Rotor Polarity Detection and Sensorless Control of PM Synchronous Machines,” Conference Record of the 2006 IEEE Industry Applications Conference Forty-First IAS Annual Meeting, 8 10 2006 .

Claims

Claims: A method for measuring the magnetic saturation profiles of a synchronous machine, comprising a rotor and a stator, wherein the synchronous machine is controlled by pulsed terminal voltages according to the pulse width modulation method and the current of the synchronous machine is measured cyclically, characterized in that macroscopic flux pulses are applied which cause the motor current to briefly increase to a magnitude that can change the magnetic saturation state of the motor. A method according to claim 1, characterized in that the values ​​of the respective applied flux pulse and the resulting measured current are stored together as an operating point data pair in a table. A method according to claim 1 or 2, characterized in that several microscopic, i.e.,Non-relevant saturation-changing flux pulses are injected, which are distinct from one another, sum to zero, and form an injection pattern in their shape and arrangement. A method according to claim 3, characterized in that all microscopic flux pulses have the same magnitude and are orthogonal or antiparallel to each other, such that the injection pattern is a square. A method according to claim 3 or 4, characterized in that the entries of the local admittance or inductance are calculated from the current response to the injection pattern, added to the operating point data pair, and stored. A method according to any one of claims 2 to 5, characterized in that a plurality of macroscopic flow pulses with different d and q components are impressed and the resulting operating point data pairs are stored in the table. A method according to any one of the preceding claims, characterized in that each of the macroscopic flow pulses is followed by a corresponding compensation pulse which has the same d component and a negated q component in order to minimize the resulting angular momentum. A method according to any one of the preceding claims, characterized in that, prior to each macroscopic flux pulse, a direct current on the order of the motor's rated current is applied in a defined direction until the resulting oscillation has subsided and the rotor is aligned with the current. A method according to any one of claims 2 to 8, characterized in that simple rotor position assignment parameters are calculated from the entries in the table by means of interpolation. A method according to any one of claims 2 to 9, characterized in that unique rotor position assignment parameters are derived from the entries in the table by means of interpolation and SFC calculation.Device for controlling and regulating a rotating field machine, comprising a stator and a rotor, with a controllable PWM converter for outputting pulsed terminal voltages, with a device for detecting a number of phase currents, and with a controller for controlling the PWM converter, which is configured and designed to carry out the method according to one of the preceding claims. Synchronous machine, comprising a stator and a rotor with or without permanent magnets, with a device for controlling and / or regulating according to claim 10.

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